Electronically operated remote control systems, such as garage door opener systems, home security systems, home lighting systems, gate controllers, etc., typically employ a portable, hand-held transmitter (i.e., an original transmitter) to transmit a control signal to a receiver located at the remote control system. For example, a garage door opener system typically includes a receiver located within a home owner's garage and coupled to the garage door opener. A user presses a button on the original transmitter to transmit a radio frequency signal to the receiver to activate the garage door opener to open and close a garage door. Accordingly, the receiver is tuned to the frequency of its associated original transmitter and demodulates a predetermined code programmed into both the original transmitter and the receiver for operating the garage door. To enhance security of wireless control systems, such as a garage door opener system, manufacturers commonly use encryption technology to encrypt the radio frequency signal sent from a transmitter to a receiver. One such encryption method is a rolling code system, where each digital message sent from the transmitter to the receiver has a different code from the previous digital message.
As an alternative to a portable, hand-held original transmitter, a trainable transmitter or transceiver may be provided in a vehicle for use with remote control systems. A trainable transmitter or transceiver is configurable by a user to activate one or more of a plurality of different remote control system receivers using different radio frequency messages. A user may train the trainable transmitter to an existing original transmitter by holding the two transmitters in close range and pressing buttons on the original transmitter and the trainable transmitter. The trainable transmitter identifies the type of remote control system (e.g., fixed or rolling code) associated with the original transmitter based on a radio frequency signal received from the original transmitter. The trainable transmitter may then identify and store the control code and RF carrier frequency of the original transmitter radio frequency control signal. In addition, the receiver may learn a transmitter identifier of the trainable transmitter. For systems employing a rolling code (or other encryption method), the trainable transceiver and receiver must also be “synchronized” so that the counters of the trainable transmitter and the receiver begin at the same value. Accordingly, the user presses a button on the remote control system receiver to put the receiver in a training mode. A button on the trainable transceiver may then be pressed, for example, two to three times, to transmit messages so the receiver may learn the transmitter identifier, complete synchronization of the receiver and the trainable transmitter and confirm that training was successful. Once trained, the trainable transceiver may be used to transmit RF signals to control the remote control system.
During training, the accuracy of the frequency learned and stored by the trainable transmitter depends on the frequency of the control signal transmitted by the original transmitter. The frequency of the original transmitter signal may be, for example, lower than intended due to sources of error at the original transmitter. In addition, error in the learned frequency may be introduced during the training process. During training, it may also be difficult to know the desired frequency of a fixed code system due to the number of fixed code systems which have different operating frequencies. Typically, while training to a fixed code system, the system manufacturer (or brand of system) is not identified by the trainable transceiver. Rather, the control code and frequency of the signal received from the original transmitter is determined and then stored. As a result, if frequency snapping is used while training to a fixed code system, it may be possible to inadvertently “snap off” the desired frequency of operation and adversely affect performance. In contrast, while training to a rolling code system, the system manufacturer is typically identified based on the received original transmitter control signal in order to determine the appropriate rolling code data (e.g., encryption key, etc.) for the remote control system.
There is a need, therefore, for a system and method to shift, “snap” or change the frequency learned from an original transmitter control signal to the intended carrier frequency for the remote control system being trained to during training of the trainable transmitter. There is also a need for a system and method that only shifts, “snaps” or changes the frequency learned from an original transmitter control signal when training to a rolling code system.